A userfriendly prothesis for full arm replacement ith more than four active axes

A new full arm have been designed and produced to fill the gap in the rehabilitative devices commercially available for the upper limb amputees. The main features of this system are the low weight, low noise, wide working area, and a user friendly approach to its command. The artificial limb is characterized by many servo actuated axes: two for the shoulder, one for the elbow, one for the wrist and at least one for the hand. This multi-axes architecture excludes any chance to use the sequential approach to the joints motion usually adopted in current active arm prostheses. In order to reduce the mental load, to the subject is only required to focus on the hand motion, driving it without taking into account any other part of the limb kinematic chain. Knowing the target of the hand, the system automatically manages the joints' motion: a central unit synchronizes the axes motion in order to follow the target as fast as possible and peripheral units control separately each brushless motor law of motion. The motors are controlled by two closed loop, in velocity and position using as references the hall sensors; soft stops are also guaranteed by the software. The system follows the requests of the subject changing the motion target during the movement. At present the hand is driven by the patient by means of the head, only the grasping function is directly obtained by processing electromyographic signals. The head kinematics is detected by means of mems accelerometers and gyroscopes. Recent tests have shown that the distance from the hand to the head can be profitably driven, without increasing the subject pressure, also by means an extra electro-mechanical or electro-miographic sensor. In the new model of the prosthesis, presently under test, the mechanical and electrical component have been fully redesigned to better fulfill the patients requests.